1. Technical Field
The present invention relates to a position detector, and a liquid ejecting apparatus incorporating the same.
2. Related Art
In an ink jet printer, a carriage and a printed subject such as paper are driven by a motor. Incidentally, in order to perform position control and speed control, an encoder is generally used. The encoder includes a photo sensor and a scale. The photo sensor includes a light emitting element and a light receiving element the scale includes a light transmitting section which transmits light emitted from the light emitting element, and a light shielding section which shields light emitted from the light emitting element. These light transmitting section and light shielding section are repetitively arranged at a fixed pitch to form an array (hereinafter, referred to as an light receiving element array).
In such the encoder, recently, there is a problem of attachment of ink mist. Namely, recent printers which perform printing with high precision can eject minute ink droplets from a printing head. These minute ink droplets readily become ink mist and drift inside the printer. Therefore, as such the printer is used for a while, solidified ink mist is piled on the scale.
Japanese Patent Publication No. 2005-81691A (JP-A-2005-81691) teaches that a partition member is arranged between a carriage belt and a scale to prevent the attachment of the ink mist onto the scale. Japanese Patent Publication No. 2004-202963A (JP-A-2004-202963) discloses a configuration for correcting, in a case where duty factor of a signal outputted from a light receiving element decreases due to the attached ink mist, the duty factor of the output signal so as to become 50%.
Incidentally, the light emitting element is arranged such that the optical axis thereof is located at the center of the light receiving element array. With such an arrangement, when light passes through the light transmitting section of the scale at the end of the array of the light receiving elements, the light travels in a direction oblique with respect to the optical axis. Therefore, there is an increase in the percentage of the light having passed through the light transmitting section of the scale being received not by a light receiving element opposing the light transmitting section but by a light receiving element adjacent thereto, which is covered with a light shielding section.
As mentioned above, when there is increased the quantity of light entering the light receiving element covered with the light shielding section at the end of the light receiving element array, an accurate encoder signal cannot be obtained, which in turn induces a detection failure. When ink mist has adhered to the light transmitting section as mentioned above, there may arise a case where diffraction of light or the like is induced by adhesion of ink mist. Accordingly, a detection failure becomes more likely to arise.
In JP-A-2005-81691, the flow of ink mist is restricted by placing a partition member, to thus prevent adhesion of ink mist to the scale. However, this document does not disclose any means effective for preventing the light receiving element covered with a light shielding section from receiving undesired light (i.e., a detection failure).
JP-A-2004-202963 discloses a configuration for correcting a signal. However, this document does not disclose any means effective for preventing the light receiving element covered with the light shielding section from receiving undesired light either.